Conductance Study of the Thermodynamics of Tl+ ion Complexes with Different 18-Membered Crown Ethers in Binary Dimethylformamide-Acetonitrile Mixtures

A conductance study of the interactionbetween Tl⁺ ion and 18-crown-6 (18C6),dicyclohexano-18-crown-6 (DC18C6), benzo-18-crown-6(B18C6), diaza-18-crown-6 (DA18C6),dibenzyldiaza-18-crown-6 (DBzDA18C6) andhexaaza-18-crown-6 (HA18C6) indimethylformamide-acetonitrile mixtures was carriedout at various temperatures. The formation constantsof the resulting 1 : 1 complexes were determined fromthe molar conductance-mole ratio data and found tovary in the order HA18C6 > DA18C6 > DBzDA18C6 >18C6 > DC18C6 > B18C6. The enthalpy and entropy ofthe complexation reactions were determined from thetemperature dependence of the formation constants.     

Conductance Study of Binding of Some Rb+ and Cs+ Ions by Macrocyclic Polyethers in Acetonitrile Solution

A conductance study of the interaction between Rb+ and Cs+ ions and18-crown-6 (18C6), dicyclohexyl-18-crown-6 (DC18C6), dibenzo-18-crown-6 (DB18C6),dibenzo-24-crown-8 (DB24C8), and dibenzo-30-crown-10 (DB30C10) inacetonitrile solution has been carried out at various temperatures. The formationconstants of the resulting 1:1 complexes were determined from the molarconductance-mole ratio data and found to vary in the orderDC18C6 > 18C6 > DB30C10 > DB18C6 DB24C8for Rb+ ion andDC18C6 > 18C6 > DB30C10 DB24C8 > DB18C6for Cs+ ion. The enthalpy and entropy of complexation were determined fromthe temperature dependence of the formation constants. The complexes with the18-crowns are both enthalpy and entropy stabilized while, in the case of largecrown ethers, the corresponding complexes are enthalpy stabilized but entropydestabilized.     

Conductance Study of the Thermodynamics of Complexation of K+, Rb+, Cs+ and Tl+ Ions with Dibenzo-24-crown-8 in Binary Acetonitrile–Nitromethane Mixtures

The complexation reactions between dibenzo-24-crown-8 (DB24C8) and K⁺, Rb⁺, Cs⁺ and Tl⁺ ions were studied conductometrically in different acetonitrile–nitromethane mixtures at various temperatures. The formation constants of the resulting 1:1 complexes were calculated from the computer fitting of the molar conductance–mole ratio data at different temperatures. At 25 °C and in all solvent mixtures used, the stability of the resulting complexes varied in the order Tl⁺ > K⁺ > Rb⁺ > Cs⁺. The enthalpy and entropy changes of the complexation reactions were evaluated from the temperature dependence of formation constants. It was found that the stability of the resulting complexes increased with increasing nitromethane in the solvent mixture. The TΔS° vs. ΔH° plot of all thermodynamic data obtained shows a fairly good linear correlation indicating the existence of enthalpy–entropy compensation in the complexation reactions.     

Conductance Study and Thermodynamics of Some Substituted Ammonium Salts with Crown Ethers in Aqueous Solution

A conductance study of the interaction between substituted ammonium ions with three crown ethers in aqueous solution has been carried out at different temperatures. The formation constants of the 1 : 1 complexes at various temperatures were determined from the molar conductance-mole ratio data and found to vary in the order 18C6 > 15C5 > 12C4 for the same salt and with the same crown, the formation constants vary in the order (C2H5)3NHCl > (C2H5)4NBr > (CH3)3NPhI.The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants. The results indicate that the complexation process is enthalpy unfavored and entropy favored. The influence on the thermodynamic data for different parameters such as cavity size of crown ethers and nature of salt are discussed.     

A Polarographic Study of Tl + , Pb 2 and Cd 2+ Complexes with Dicyclohexano-18-Crown-6 in Some Binary Mixed Solvents

The complexes of Tl⁺, Pb²⁺ and Cd²⁺ cations with the macrocyclic ligand, dicyclohexano-18-crown-6\linebreak(DC18C6) were studied in water/methanol (H₂₊O/MeOH), water/1-propanol (H₂₊O/1-PrOH), water/acetonitrile (H₂₊O/AN), water/dimethylformamide (H₂₊O/DMF), dimethylformamide/acetonitrile (DMF/AN), dimethylformamide/methanol (DMF/MeOH), dimethylformamide/1-propanol (DMF/1-PrOH) and dimethylformamide/nitromethane (DMF/NM) mixed solvents at 22 °C using differential pulse polarography (DPP), square wave polarography and conductometry. In general, the stability of the complexes was found to decrease with increasing concentration of water in aqueous/non-aqueous mixed solvents with an inverse relationship between the stability constants of the complexes and the concentration of DMF in non-aqueous mixed solvents. The results show that the change in stability of DC18C6.Tl⁺, vs the composition of solvent in DMF/AN and DMF/NM mixed solvents is apparently different from that in DMF/MeOH and DMF/1-PrOH mixed solvents. While the variation of stability constants of the DC18C6.Tl⁺ and DC18C6.Pb²⁺ complexes vs the composition of H₂₊O/AN mixed solvents is monotonic, an anomalous behavior was observed for variations of log K_f vs the composition of H₂₊O/1-PrOH and H₂₊O/MeOH mixed solvents. The selectivity order of the DC18C6 ligand for the cations was found to be Pb²⁺ > Tl⁺ > Cd²⁺.     

Conductance and Thermodynamic Study of the Interaction of Some Transition and Heavy Metals with Phenyl-aza-15-crown-5 (PhA15C5) in Different Binary Acetonitrile-Water Solvent Mixtures

A conductance study of the interaction between Fe(ClO4)3, Cu(ClO4)2, Fe(NO3)3, Cu(NO3)2, Hg(NO3)2 and Cd(NO3)2 with phenyl-aza-15-crown-5 (PhA15C5) in different acetonitrile-water mixtures has been carried out at various temperatures. The formation constants were determined at various temperatures. It was found that the stability of the nitrate salts decreases in the order Hg2+ > Cu2+ > Fe3+ > Cd2+ and the formation constants decrease as the percentage of acetonitrile decreases in the mixture. The counter anion also affects the stability of the complexes, where the metal perchlorate-crown complexes are more stable than those of the metal nitrate salts. The enthalpy and entropy of the complexation were calculated and were found to be sensitive to solvent composition.     

A Polarographic Study of Tl+, Pb2+ and Cd2+ Complexes with Aza-18-crown-6 and Dibenzopyridino-18-crown-6 in some Binary Mixed Non-aqueous Solvents

The complexation of Tl⁺, Pb²⁺and Cd²⁺ cations by macrocyclic ligands, aza-18-crown-6 (L1) and dibenzopyridino-18-crown-6 (L2) was studied in some binary mixtures of methanol (MeOH), n-propanol (n-PrOH), nitromethane (NM) and acetonitrile (AN) with dimethylformamide (DMF) at 22 °C using DC (direct current) and differential pulse polarographic techniques (DPP). The stoichiometry and stability constants of the complexes were determined by monitoring the shifts in half-waves or peak potentials of the polarographic waves of metal ions against the ligand concentration. In all of the solvent systems, the stability of the resulting 1:1 complexes was found to be L1 > L2. The selectivity order of the L2 ligand for the cations was found to be Pb²⁺ > Tl⁺ > Cd²⁺ and the selectivity of the L1 ligand for Pb²⁺ ion was greater than that of Tl⁺ ion. The results show that the stability of the complexes depends on the nature and composition of the mixed solvents. There is an inverse relationship between the stability constants of the complexes and the amount of dimethylformamide in the mixed solvent systems.     

Complex Formation of Crown Ethers with Cations in Water–Organic Solvent Mixtures. III. Thermodynamics of Interaction Between Na+ Ion with 15-Crown-5 Ether in Water–Acetonitrile Mixtures at 25°C

Enthalpies of solution of 15-crown-5 ether in the acetonitrile–water–sodium iodide system have been measured at 25°C. The equilibrium constants of complex formation of 15C5 with sodium iodide have been determined by molar conductance at various mole ratios 15C5 to sodium iodide in mixtures of water with acetonitrile at 25°C. The thermodynamic functions for complexation of the crown ether with Na⁺ were calculated. From the result, the standard Gibbs energies of complex formation as a function of the normalized Lewis acidity parameters E ^N _T and enthalpy of solvation of 15C5 in the mixtures of water with acetonitrile have been analyzed. The enthalpies of transfer of the 15C5 complex with sodium iodide from pure acetonitrile to the mixtures studied were calculated and discussed.     

Conductance study of the thermodynamics of ammonium ion complexes with several crown ethers in acetonitrile solution

A conductance study concerning the interaction between ammonium ion and several crown ethers in acetonitrile solution has been carried out at different temperatures. The stability constants of the resulting 11 complexes at various temperatures were determined from the molar conductance-mole ratio data and found to vary in the order DC18C6>18C6>DB30C10>DB21C7>DB24C8>DB18C6>15C5>B15C5. The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants. The influence on the thermodynamic data of different parameters such as cavity size and dimensionality of crown ethers, nature of substituents in the polyether ring, conformations of the free and complexed ligands, solvent-ligand interaction and number of N–H bonds available for hydrogen bonding are discussed.     

A Conductometric Study of Complexation Reactions Between Dibenzo-18-Crown-6 (DB18C6) with Cu2+, Zn2+, Tl+ and Cd2+ Metal Cations in Dimethylsulfoxide–Ethylacetate Binary Mixtures

The complex formation between Cu²⁺, Zn²⁺, Tl⁺ and Cd²⁺ metal cations with macrocyclic ligand, dibenzo- 18-crown-6 (DB18C6) was studied in dimethylsulfoxide (DMSO)–ethylacetate (EtOAc) binary systems at different temperatures using conductometric method. In all cases, DB18C6 forms 1:1 complexes with these metal cations. The stability constants of the complexes were obtained from fitting of molar conductivity curves using a computer program, Genplot. The non-linear behaviour which was observed for variations of log K _f of the complexes versus the composition of the mixed solvent was discussed in terms of changing the chemical and physical properties of the constituent solvents when they mix with one another and, therefore, changing the solvation capacities of the metal cations, crown ether molecules and even the resulting complexes with changing the mixed solvent composition. The results show that the selectivity order of DB18C6 for the metal cations in pure ethylacetate and pure dimethylsulfoxide is: Tl⁺ > Cu²⁺ > Zn²⁺ > Cd²⁺ but the selectivity order is changed with the composition of the mixed solvents. The values of enthalpy changes (ΔH°_C) for complexation reactions were obtained from the slope of the van’t Hoff plots and the changes in standard enthalpy (ΔS°_C) were calculated from the relationship: ΔG°_C,298.15=ΔH°_C − 298.15 ΔS°_C. The obtained results show that in most cases, the complexes are enthalpy stabilized, but entropy destabilized and the values of ΔH°_C and ΔS°_C depend strongly on the nature of the medium.     

Complex Formation of Crown Ethers with Cations in the Water–Organic Solvent Mixtures. Part VIII.1 Thermodynamic of Interactions of Na+ Ion with 15-Crown-5 and Benzo-15-Crown-5 Ethers in the Mixtures of Water with Hexamethylphosphortriamide at 298.15 K

The equilibrium constants of complex formation of 15-crown-5 and benzo-15-crown-5 ethers with the sodium cation have been determined by conductivity measurements. The enthalpic effect of complex formation has been measured by a calorimetric method at 298.15 K. The thermodynamic functions of complex formation of 15-crown-5 and benzo-15-crown-5 ethers with the sodium cation in the mixtures of water with hexamethylphosportriamide at 298.15 K have been calculated. The extent of complex formation in this mixed solvent depends on the enthalpic effect. In water–hexamethylp- hosportriamide mixtures with medium and low water content, the complex of crown ethers with the sodium cation is not formed because of the strong solvation of sodium cation and crown ethers molecules; this implies that the entropy of complex formation is more negative than the enthalpy of complex formation.     

Lithium-7 NMR Study of Several Li+-Crown Ether Complexes in Binary Acetone-Nitrobenzene Mixtures

⁷Li NMR measurements were employed to monitor the stoichiometry andstability of Li⁺ ion complexes with 12-crown-4 (12C4), 15-crown-5 (15C5), benzo-15-crown-5 (B15C5) l8-crown-6 (18C6), dicyclohexano-18-crown-6 (DC18C6) and dibenzo-18-crown-6 (DB18C6) in binary acetone-nitrobenzene mixtures of varying composition. In all cases studied, the variation of ⁷Li chemical shift with the crown/Li⁺ mole ratio indicated the formation of 1:1 complexes. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data to an equation that relates the observed chemical shifts to the formation constant. In all solvent mixtures used, the stabilities of the resulting 1:1 complexes varied in the order15C5 > B15C5 > DC18C6 > 18C6 > 12C4 >DB18C6. It was found that,in the case of all complexes, an increase in the percentage of acetone in thesolvent mixtures significantly decreased the stability of the complexes.     

Fencing of Photoinduced Electron Transfer in Nonconjugated Bichromophoric System by β-cyclodextrin Nanocavity

²³Na NMR measurements were employed to monitor the stability of Na⁺ ion complexes with 18-crown-6 (18C6), dicycloxyl-18-crown-6 (DC18C6), dibenzo-18-crown-6 (DB18C6), 15-crown-5 (15C5) and benzo-15-crown-5 (B15C5) in binary acetonitrile–dimethylformamide mixtures of varying composition. In all cases, the variation of ²³Na chemical shift with [crown]/[Na⁺] mole ratios indicated the formation of 1:1 complexes. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data to an equation which relates the observed chemical shifts to the formation constants. It was found that, in pure acetonitrile, the stabilities of the resulting 1:1 complexes vary in the order 15C5>DC18C6>B15C5>18C6>DB18C6, while in pure dimethylformamide the stability order is DC18C6>18C6>15C5>B15C5>DB18C6. The observed changes in the stability order could be related to the specific interactions between some crown ethers and acetonitrile. It was found that, in the case of all complexes, an increase in the percentage of dimethylformamide in the solvent mixtures would significantly decrease the stability of the complexes.     

Complex Formation of Crown Ethers with the Cucurbit[6]uril–Spermidine and Cucurbit[6]uril–Spermine Complex in Aqueous Solution

Alkyl amines are able to form complexes with either crown ethers or cyclodextrins or cucurbit[6]uril. The same is known for polyamines such as spermidine and spermine. However, the simultaneous formation of such polyamines with crown ethers and cucurbit[6]uril has not been studied. The ability of polyamines such as spermidine and spermine to form mixed complexes with different ligands, e.g. crown ethers and cucurbit[6]uril has been studied in aqueous solution using pH-metric and calorimetric titrations. The thermodynamic data of reaction between crown ethers with spermidine, spermine and their cucurbit[6]uril complexes have been determined. The presence of cucurbit[6]uril on the polyamines has no important influence upon the reaction of these amines with crown ethers. The reactions between polyamines, cucurbit[6]uril and crown ethers are simple examples for the self organization of molecules due to specific interactions. Received in final form: 26 January 2005     

Conductance study of complex formation of thallium and silver ions with several crown ethers in acetonitrile,acetone and dimethylformamide solutions

The complexation reactions between Tl⁺ and Ag⁺ ions and several crown ethers have been studied conductometrically in acetonitrile, acetone and dimethylformamide solutions at 25°C. The stability constants of the resulting 1:1 complexes were determined, and found to decrease in the order DA18C6>DC18C6>DB30C10>18C6>DB21C7>DB24C8>DB18C6>B15C5 >12C4, in the case of Tl⁺ complexes, and in the order DA18C6>DC18C6>18C6>DB18C6 >DB24C8>DB30C10B15C5>DB21C7 for Ag⁺ complexes. There is an inverse relationship between the stabilities of the complexes and the Gutamnn donicity of the solvents. The influence of a number of atoms in the macrocycle and of substituents in the polyether ring on the stability of the complexes is discussed.     

Study of Bulk Membrane Transport of Some Heavy Metal Cations Using Three Macrocyclic Ligands Containing Oxygen and Nitrogen Heteroatoms

The transport experiments of Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Ag⁺ and Pb²⁺ metal cations were carried out by dibenzo-18-crown-6 (DB18C6), dibenzyl-diaza-18-crown-6 (Dibenzyl-diaza-18C6) and di-tert-butyl-dibenzo-18-crown-6 (Di-tert-butyl-DB18C6) using chloroform (CHCl₃), 1,2-dichloroethane (1,2-DCE) and nitrobenzene (NB) organic solvents as liquid membranes. The source phase contained equimolar concentration of these metal cations and the source and receiving phases being buffered at pH=5 and pH=3, respectively. The obtained results show that the selectivity and the efficiency of transport for these heavy metal cations change with the nature of the ligand and also the organic solvents, which were used as liquid membranes in these experiments. A good selectivity was observed for silver (I) ion by dibenzyl-diaza-18C6 in all membrane systems. Dibenzo-18C6 and di-tert-butyl-DB18C6 showed the highest transport efficiency for cobalt (II) ion. The effect of stearic acid on transport efficiency was also investigated and the results show that the efficiency of transport of the heavy metal cations increases in the presence of this organic acid.     

The association constants of Na(+) with dibenzo[3n]crown-n in THF/water using ISE

The Na⁺ association constants, K₁₁ and β₁₂, of 1/1 and 1/2 stoichiometry of macrocycles of (1,2)dibenzo[15]crown-5, (1,3)dibenzo[18]crown-6, (1,4)dibenzo[21]crown-7, (2,3)dibenzo[21]crown-7, (2,4)dibenzo[24]-crown-8 and dicyclohexano[24]crown-8 were determined in THF/water, (50/50), mixtures. We used a Methrom Na⁺ ISE for the potentiometric measurements and applied the 1/(β_nm[A_o⁺])^n+m−1=(1−nP_c)(1−mP_c)/P_c equation where the P_c=P/[1+(m−1)P] and P is the mole fraction of the complexed cation, [A_n⁺L_m] for association constants with linear best fit. Results were in well agreement with the macrocyclic size and cation radii relationships. Measurements showed the role of aromatic groups of macrocyclics in THF/water (50/50) which allowed the macrocyclic molecules more selectively bind Na⁺ compared to the associations those obtained in water.     

Synthesis and Host Properties of (1,3)- p-tert-Butylcalix[5]crown-6 Derivatives Incorporating the 1,1'-Binaphthalene-2,2'-dioxy Subunit

Alkylation of p-tert-butylcalix[5]arene (1) with 2,2'-bis(5-tosyloxy-3-oxa-1-pentyloxy)-1,1'-binaphthalene ((±)-2) in the presence of CsF affords selectively racemic 1,3-bridged calix[5] [5]crown-6-triol 3, along with very small amounts of the (1,2)-bridged regioisomer 4. Compound 3 has been converted into tri-methoxy and tri--picolyloxy derivatives 5 and 6, respectively, by exhaustive alkylation with the appropriate electrophile and base. The direct separation of the enantiomers of racemates 3 and 6 was achieved by HPLC, using a chiral stationary phase (Chiralpak AD). Hosts 5 and 6 are able to selectively form 1 : 1 endo-cavity complexes with the linear RNH₃ ⁺ ions.     

An NMR study of the stoichiometry and stability of lithium ion complexes with 12-crown-4, 15-crown-5 an 18-crown-6 in binary Acetonitrile-Nitrobenzene mixtures

Proton NMR spectroscopy was used to study the complexation reaction between lithium ion and 12-crown-4, 15-crown-5 and 18-crown-6 in a number of binary acetonitrile-nitrobenzene mixtures. In all cases the exchange between free and complexed crowns was fast on the NMR time scale and only a single population average¹H signal was observed. Formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift-mole ratio data. There is an inverse relationship between the complex stability and the amount of acetonitrile in the mixed solvent. It was found that, in all solvent mixtures used, 15-crown-5 forms the most stable complex with Li⁺ ion in the series.     

Conductance study of the thermodynamics of some transition and heavy metal cryptates in binary acetonitrile-dimethylsulfoxide mixtures

A conductance study of the interaction between Co²⁺, Ni²⁺, Cu²⁺, Cd²⁺, Zn²⁺ and Pb²⁺ ions with cryptands C211, C221 and C222 in different acetonitrile-dimethylsulfoxide mixtures has been carried out at various temperatures. The formation constants of the resulting metal cryptates were determined from the molar conductance-mole ratio data. It was found that the stability of Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ cryptates vary in the order C211>C221>C222, while for Cd²⁺ cryptates the stability order is C221>C222>C211. A linear relationship is observed between logK _f of different metal cryptates and the mole fraction of acetonitrile in the solvent mixture. The enthalpy and entropy of cryptate formation reactions were determined from the temperature dependence of the formation constants. The enthalpy and entropy changes are quite sensitive to the solvent composition and the resultingTS ⁰–H ⁰ plot shows a fairly good linear correlation, indicating the existence of an entropy-enthalpy compensation in the cryptate formation reactions. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82181 (30 pages).